Curable epoxy resin compositions containing phthalamic acid-type curing agents

ABSTRACT

Certain phthalamic acid compounds are used as latent hardeners for epoxy resin materials. The hardener effect is achieved by curing at elevated temperatures. The compositions are useful as adhesives and in coating applications.

United States Patent [72] inventors Raymond Michael Moran, Jr.

Brick Town;

Robert Paul Kretow, Lakewood, both of NJ.

Nov. 28, 1969 Dec. 14, 1971 Ciba Corporation Summit, NJ.

Appl. No. Filed Patented Assignee CURABLE EPOXY RESIN COMPOSITIONSCONTAINING PI'ITHALAMIC ACID-TYPE CURING AGENTS 7 Claims, No DrawingsUS. Cl 260/47 CA, ll7/l6l ZB, 260/2 EA, 260/18 EP, 260/37 EP,

zap 73.4 EP, 260/8835. 260/913 3,l40,299 7/l964 Loncrini 260/47EPXPrimary ExaminerWilliam M. Short Assistant Examiner--T. PertillaAuorneysHarry Goldsmith. Joseph G. Kolodny and Mario A. Monaco ABSTRACT:Certain phthalamic acid compounds are used as latent hardeners for epoxyresin materials. The hardener effect is achieved by curing at elevatedtemperatures. The compositions are useful as adhesives and in coatingapplications.

CURABLE EPOXY RESIN COMPOSITIONS CONTAINING PIITIIALAMIC ACID-TYPECURING AGENTS BACKGROUND OF THE INVENTION This invention relates to thecuring of epoxy resins. More particularly, it relates to the discoveryof a class of compounds useful in the curing of epoxides to producematerials useful as high-temperature adhesives, castings, moldings andpowder coatings.

There are a great many forms'of epoxide resins available today, many ofwhich can be cured by various means to provide final products tailoredto a specific end use. Thus, solid, infusible resins have been preparedin this manner using a variety of amines as curing agents. Similarly,soft, flexible products have been obtained using certain metal salts ascuring agents for some polyepoxides.

Epoxy systems normally are comprised of at least two compounds, one ofwhich is the epoxy resin, and the other a hardener. These componentsmust be stored separately, however, prior to use to prevent reaction toa cured or infusible state. In the production of cured epoxides, it issometimes desirable to provide a mixture which will not cure undernormal ambient conditions, but will remain as a stable blend for areasonable period of time. Activation of such a mixture to a curedstate, desirably, is then achieved by curing at an elevated temperature.The mixture should have a cure time at an elevated temperature that willnot be oppressive from an economic point of view, but should not be sorapid as to prevent adequate working time. In addition to thesecharacteristics, the resulting cured product should possess goodphysical and mechanical qualities so as to function in an acceptablemanner. The art has not been altogether successful in achieving theseresults for various reasons. Thus, while a stable resin hardener mix maybe obtained, the resulting blend is not always curable under reasonableconditions of time and temperature. Often, if curable, the blend is notcured to an entirely suitable state. Therefore, the art is continuouslysearching for new and improved hardener materials.

A new class of compounds has now been discovered which when blended withvarious epoxides results in a relatively stable mixture under normalconditions, but which because of latent hardening capabilities, exerts acuring effect on the epoxides at elevated temperatures. Such compoundsmay be described as phthalamic acid compounds of the formula CONHR,

wherein R is hydrogen alkyl, aminoalkyl,. phenyl,

aminophenyl, alkylphenyl, alkoxyphenyl, benzyl alkylbenzyl,

alkoxybenzyl, aminobenzyl, or pyridyl, and R, is hydrogen orlllustrative of the foregoing R, groups are methyl, ethyl, propyl,aminomethyl, aminoethyl, aminobutyl, methylphenyl, methoxyphenyl,ethoxyphenyl, butoxyphenyl and the like. Preferred R, groups arehydrogen, 2-aminophenyl, p-methoxyphenyl, phenyl, aminomethyl, benzyl,and pyridyl. R, is preferably hydrogen, but is suitably A or B,especially when R, is aminophenyl.

Typical compounds with the above formula are ('a) phthalamic acid (R,,R, =hydrogen) (b) N-aminomethyl phthalamic acid (b,) N-(2-aminoethyl)phthalamic acid (c) N, N-bis(2-aminophenyl)-3,3',4,4'-benzophenonetetracarboxylic diacid-diamide (d) N-benzyl phthalamicacid (e)N-2-pyridyl phthalamic acid (f) N-phenyl phthalamic acid (phthalanilicacid) (g) N, N'-bis( 2-aminophenyl)-3,3'-(2-acetoxy-l ,3- glycerol)bistrimellitic acid-amide (h) N-(p-methoxyphenyl) phthalamic acid Variousconditions of cure time and temperature, and the physical properties ofthe cured resin will, of course, vary from compound to compound. Ingeneral, however, the epoxy compounds to be cured are those possessingmore than one epoxide group and may be aliphatic, cycloaliphatic,aromatic, and the like, and may carry inert substituents such as chloroand others well known and encountered in the art, and may be monomers orpolymeric. They may also contain ether linkages and ester groups aswell. Especially preferred are epoxides prepared from Bisphenol A, aphenol or cresol and epichlorhydrin, although virtually any epoxideproduced from a polyhydric alcohol and epichlorhydrin maybe used.Preferably, epoxides having an epoxy value of 0.3 to 0.7 equivalent perg. of material are suitable. Typical epoxides are those produced fromepichlorhydrin and a polyhydric phenol or alcohols such as resorcinol,catechol, 1,2,6-hexanetriol, sorbitol, mannitol pentaerythritol,trimethylolpropane, glycerol allyl ether. Similarly, polymeric materialscontaining polyhydric hydroxyls such as appropriately substitutedpolyethers and polyesters may likewise be employed. For example, theremay be employed vinyl cyclohexene dioxide, epoxidized mono-, diandtriglycerides, butadiene dioxide, l,4-bis (2,3-epoxypropoxy) benzene,4,4-bis (2,3-epoxypropoxy) diphenyl ether, l,8-bis (2,3-epoxypropoxy)octane, l,4-bis (2,3-epoxypropoxy).cyclohexane, 4,4-bis (2-hydroxy-3,4-epoxybutoxy) diphenyldimethylmethane, 1,3-bis (4,5- epoxypentoxy)S-chlorobenzene, l,4-bis (3,4-epoxybutoxy) 2-chlorocyclohexane, ethyleneglycol diglycidyl ether, resor cinol diglycidyl ether,l,2,5',6-diepoxyhexyne-3, l,2,5,6- diepoxyhexane and l,2,3,4-tetra(2-hydroxy-3,4-epoxybutoxy) butane.

Other examples include the glycidyl polyethers of polyhydric phenolsobtained by reacting a polyhydric phenol with an excess, e.g. 4 to 8 molexcess, of a chlorohydrin, such as epichlorohydrin and diglycerolchlorohydrin. Thus, a polyether, which is substantially diglycidyl etherof 2,2-bis (2,3-epoxypropoxyphenyl) propane is obtained by reactingbisphenol 2,2-bis (4-hydroxyphenyl) propane with an excess ofepichlorohydrin in an alkaline medium. Other polyhydric phenols that canbe used for this purpose include resorcinol, catechol, hydroquinone,methyl resorcinol, or polynuclear phenols, such as 2,2-bis(4-hydroxyphenyl) butane, 4,4- dihydroxybenzophenone, bis(4-hydroxyphenyl) ethane, and l ,S-dihydronaphthalene.

Still a further group of the polyepoxides comprises the polyepoxypolyethers obtained by reacting, preferably in the presence of anacid-acting compound, such as hydrofluoric acid, one of theaforedescribed halogen-containing epoxides with a polyhydric alcohol,and subsequently treating the resulting product with an alkalinecomponent. Polyhydric al cohols that may be used for this purposeinclude glycerol, propylene glycol, ethylene glycol, diethylene glycol,butylene glycol, hexanetriol, sorbitol, mannitol, pentanetriol,pentaerythritol, diand tripentaerythritol, polyglycerol, dulcitol,inositol, carbohydrates, methyltrimethylolpropane, 2,6-octanediol,1,2,4,5-tetrahydroxycyclohexane, 2-ethylhexanetriol-l,2,6, glycerolmethyl ether, glycerol allyl ether, polyvinyl alcohol and polyallylalcohol, and mixtures thereof. Such polyepoxides may be exemplified byglycerol triglycidyl ether, mannitol, tetraglycidyl ether and sorbitoltetraglycidyl ether.

A further group of the polyepoxides comprises the polyepoxy polyestersobtained by esterifying a polycarboxylic acid with an epoxy'containingalcohol, such as, for example, the diglycidyl ester of adipic acid, thediglycidyl ester of malonic acid, and the diglycidyl ester of succinicacid.

Typically, the benefits of the invention are obtained by blending thehardener with the epoxides, usually employing standard blendingequipment known in the art, together with any other adjuvants desired,and then when ready for use in service, by activating the hardener. Ingeneral, the amount of hardener used will be at or near thestoichiometric amount required for the specific ingredients. Usually,this will range from about 15 to 75 parts of hardener per hundred partsof resin (phr). For the preferred compositions of the invention, thisrange will be about 15 to 50 phr.

The conditions of time and temperature used for cure ordinarily aspreviously stated, will vary from blend to blend. In general, however,elevated cure temperatures ranging from 130 to 170 C. and preferably 140to 160 C. will produce physically desirable resin products within 30minutes to hours, and usually within 2 hours. Of course, these cures canbe effected in the same attitude as the end use where the physicalconditions permit. Most preferably, the cures are effected by apreliminary gel period at a low temperature followed by storage for asomewhat longer period at a more elevated temperature. Best results areobtained by an initial gelling at around 90 to 100 C. followed byheating at around 130 to 170 C. for 1/2 to 5 hours, for example. Solidresins are generally slower curing than liquid resins and may requirethe use of chemical accelerators or less preferably higher temperatureor longer cure times. it is not, under most circumstances, ordinarilydesired to raise the curing temperature to accelerate these timesbecause in so doing there is a tendency for the reaction mixture tofoam. Therefore, it is preferred to use such chemical accelerators asisoniazid, dicyandiamide, imidazole, and the like. These are usuallyemployed at levels from about 0.1 to 5 phr, and preferably 0.5 to 3 phr.Other adjuvants such as fillers, coloring agents and the like, typifiedby silica, pumice, pigments and the like, may also be used.

The products of the present invention are stable prior to cure forrelatively long periods of time under normal conditions. It is notunusual for the blend to remain latent or dormant for periods of monthsor more when stored at 25 C. However, storage times longer than 3 monthsat temperatures of 40 C and higher should be avoided.

The cured products obtained from the composition of this invention findapplication in a variety of areas including high temperature adhesives,electrical potting and coating applications, and the like. Theiroutstanding dielectric properties together with good tensile andflexural properties make these materials eminently suitable forelectrical insulation applications. As such, they are quite favorablycompared to aromatic amine-cured epoxides.

Certain of the latent hardener compounds of the present invention arenovel. This is, those compounds having R equal to B, are novel and maybe prepared reacting one equivalent of 4,4'-(2-acetyl-1,3-glycerol) bisanhydro trimellitate with two equivalents of an R,-NH, compound in aninert solvent such as dimethylformamide at low temperatures, such asl050 C. and preferably 1040 C. until the reaction is complete. Suitablereaction times are l-5 hours. The reaction product is convenientlyisolated, by removal of the solvent under vacuum. For example R -NH maybe, ammonia, butylamine, 1,4- diarninobutane, 2-methylaniline, aniline,Z-aminoaniline, 2- methoxy-aniline, benzylarnine, 3-ethylbenzylamine, 2-methoxybenzylamine, Z-aminobenzylamine or 3- aminopyridine.

The following Examples are illustrative of preferred embodiments of theinvention.

EXAMPLE I Thirty-three parts by weight of N,N'-bis (2-aminophenyl)- 3,3,4,4'-benzophenone tetracarboxylic diacid diamide are blended with 100parts of a liquid epoxy resin prepared from Bisphenol A andepichlorhydrin and having an epoxy value of 0.53 equivalents per 100 g.on a three-roll mill at about 23 C,

until a smooth, pasty blend is obtained. This material can be 5 cured atelevated temperatures in a short period of time, and has the ability toretain that characteristic for over a year. This is demonstrated byobserving the amount of time required to effect gelling or hardening atthe indicated cure temperature. Such a gel-time test is as follows: l Acure plate is heated to 15010.5 C. and coated with a thin film ofrelease agent. 1.0 g.:0.1 g. of test sample is spread lightly in a 2inch X 2-inch square section on the cure plate with a back-and-forthmovement using a spatula. When the viscosity o the material increases,as noted by drag on the spatula, the spatula is removed. The point atwhich the material does not string but comes up in a film when thespatula is lifted is the end point. The time from the start is noted. vUsing this test, it is found that the initial gel time is about 8minutes at 150C. for a 1 g. mix.

At the end of one year the above material had a gel time at 150 C. of 4minutes. This indicates that the blend gels within a reasonable time forperiods up to at least one year.

EXAMPLE n The material prepared in Example 1, except that 25 phr ofhardener was used, was heated at 90 C. until it gelled and was thenpost-cured at 150 C. for 5 hours. The deflection temperature *1 on thematerial obtained was 160 C.

*1. Deflection temperature is the temperature required to deflect a 5inch X 5% inch X 5; inch slab of test material 0.010 inch under a loadof 264 p.s.i. and a temperature gradient increase of 2 C./min. This is ameasure of the thermal relaxation behavior of the material with thehigher values indicating good thermal stability.

EXAMPLE lll Following the procedure of Example 1, smooth blends areobtained using the following latent hardeners in the amount indicated inplace of the acid described in that example From the above, it can beseen that relatively short gel times are obtained from the systems, thusrepresenting products which are eminently suited for applicationswherein long elevated temperature gel times are not desirable. On theother hand, other latent hardeners of the invention have much longer geltimes at elevated temperature of the order of 2 hours, and are thussuitable for example in applications where long handling times arerequired.

EXAMPLE lV N,N'-bis (2-aminophenyl)-3,3-(2-acetoxy-l,3-glycerol bistrimellitic acid-amide 289.2 g (0.6 mol) of 4,4'-(2-acetyl-l,3-glycerol) bis anhydro trimellitate is reacted with 129.6 g of1,2-diaminobenzene (1.2 mols) in 800 mls. of dimethylformamide at below35 C. for 3 hours. The solvent is then removed under vacuum leaving abrown solid which is ground to a fine powder and air-dried. The product(410 g.) melts at 125-140" C. with decomposition and has an acid numberof 128 mg./g.

What is claimed is:

1. A latent curing resin composition capable of being cured at elevatedtemperatures comprising a l, 2 epoxy resin, and a compound having theformula CONHR1 R COOH wherein R is h ydrogejijmraminoalkyl, phenyl,

aminophenyl, alkylphenyl, alkoxyphenyl, benzyl, alkylbenzyl,alkoxybenxyl, aminobenzyl, pyridyl, and R is

2. The composition of claim 1 wherein R2 is radical A.
 3. Thecomposition of claim 2 wherein R1 is aminophenyl.
 4. The composition ofclaim 1 wherein R1 is hydrogen.
 5. The composition of claim 1 wherein R1is phenyl.
 6. The composition of claim 1 wherein R2 is the radical B. 7.The composition of claim 6 wherein R1 is aminophenyl.